The mechanisms by which polypeptide hormones, bioamines, and cAMP regulate protein synthesis will be studied using two model systems. Transcriptional regulation of prolactin and growth hormone biosynthesis by thyrotropin releasing hormone (TRH), other hormones, and dibutyryl cAMP will be studied using an established functional line of rat pituitary tumor cells (GH3). The mechanisms by which TRH and other hormones mediate increased transcription of prolactin mRNA will be defined in vitro using a cell-free protein synthesizing system derived from wheat embryos and a radiolabeled DNA probe complementary to purified prolactin mRNA. Since the product of prolactin mRNA translation is a protein larger than prolactin, referred to as preprolactin, the authenticity of this translation product, its primary structure, and the mechanism of its conversion to prolactin, will be studied in order to further define the regulatory significance of prehormones.